The present invention relates to a device for generating stitch forming data in a sewing machine by relative movement between a needle and a workpiece.
In a device for generating stitch forming data in the prior art, the stitch forming data are memorized in the memory medium of a magnetic tape or a punch tape and the memorized data are read out by driving the memory medium with a mechanical drive device in response to reading out signals in synchronization with the reciprocal movement of a sewing needle. The stitch forming data read out from the medium are applied to drive means for driving a needle and a feed device of a work as a command signal, whereby predetermined stitches are formed on the work.
However, in a reading period when the stitch forming data are applied to the driving device after the reading signals are generated, that is, in the period when the mechanical driving means drives the memory medium, if the sewing machine is driven faster than a speed at which the mechanical drive means responds to the reading signals, the stitch forming data are not read out in synchronization with the reciprocal movement of the needle.
In order to eliminate this defect, a sewing machine is known, in which a driving device is operatively connected to impart movement to a stitch forming instrumentality over said predetermined range of positions in response to stitch pattern signals. The apparatus includes a pulse generator driven in timed relation with the sewing machine for producing an effective timing pulse between stitches, a counter responsive to the timing pulses from the pulse generator for producing output control signals in a progressive numerical code, a static memory means for storing a data group capable of being summed every combination of which is unique, means responsive to the progressive numerical code of the control signals provided for extracting the data groups from the static memory, means for summing each data group extracted from said static memory, and means effective to impress on the driving device a stitch pattern signal corresponding to summation of each different data group extracted in response to said progressive numerical code of control signals (see U.S. Pat. No. 3,855,956).
In the prior sewing machine, however, the response to selection of the stitch pattern is late, because the control signals for extracting the data groups are progressive numerical codes repeatedly counted in the counter and the counter must repeatedly count for selecting one data group memorized in the static memory.